1. Field of the Invention
The present invention relates to a seamless belt, and particularly to a seamless belt which is useful as a fixing belt or an intermediate transfer belt of a high-speed electrophotographic copier and so on, or a conveyor belt.
2. Description of the Related Art
In a copier or printer including an electrophotographic copier, a fax machine, a laser beam printer and so on, a heat fixing method has been typically employed, which includes forming an image of a toner made of a thermal fusible resin on recording paper through a process of imaging electrophotographs, electrostatic records or magnetic records, and then fixing the image using heat.
A fixing device used for the heat fixing method is generally exemplified by a heat roller type fixing device for feeding recording paper on which a toner image is formed between two rollers including a heat fixing roller containing a heater and a press roller to fix the toner image. Recently, a film fixing method using a seamless belt in film form made of polyimide or polyamide imide, in lieu of the heat fixing roller, is developed and widely utilized.
In an electrostatic copying process of a color copier or color printer, in order to obtain a full color image, toner images of respective colors are formed on a photoreceptor, and sequentially transferred onto an intermediate transfer belt, thus forming a multi-color toner image on the intermediate transfer belt, which is then electrostatically transferred again onto a transfer sheet, thereby forming a color image which is not out of focus.
The polymer for the intermediate transfer belt of a color copier or the like requires flame retardancy, strength and electrical stability, and a fluorine resin or a polyimide resin is thus used. There are many cases in which such a material may be mixed with a conductive additive such as carbon black to obtain desired electrical resistance. In particular, polyimide is a material useful in terms of strength and electrostatic properties.
An example of a method of manufacturing a seamless belt such as a fixing belt or an intermediate transfer belt includes applying a polyimide precursor solution such as a polyamic acid solution on the inner surface of a tubular metal base, maintaining its thickness uniform using centrifugal force, and performing drying and imidization by heat, thus obtaining a polyimide tubular product, which is then released from the base. This method may be utilized in the production of a tubular belt having a diameter of 70˜500 mm.
Also known is a method including uniformly applying the polyimide precursor solution such as a polyamic acid solution on the outer surface of the metal base, and performing drying and imidization by heat, thus obtaining a polyimide tubular product, which is then released from the base. This method is employed only when manufacturing a tubular belt having a diameter of 70 mm or less.
If the polyimide precursor solution is applied and dried on the outer surface of the metal base to produce a tubular belt having a diameter of 70 mm or more, the adhesion area between the polyimide precursor and the metal base is large and adhesivity therebetween is strong. Upon release of the tubular belt, the tubular belt may be easily damaged. Also, after imidization of the polyimide precursor by heat, the tubular product may be contracted and is thus strongly adhered to the metal base, undesirably requiring a stronger release force. It is therefore difficult to easily release the belt product from the base.
In order to solve these problems, there have been proposed alternative methods including applying a polyimide precursor solution on a base coated with a release agent, performing heating until obtaining a strength strong enough to support at least the shape of a tubular product, releasing the product from the base, fitting the product into the base again and then burning it; and including forming small holes in a base, applying a polyimide precursor solution on the base, burning it, forcibly feeding air through such small holes from inside the base and releasing a tubular product from the base.
However, these methods cannot be utilized when manufacturing a tubular belt having a diameter of 500 mm or more, and thus there are no mass produced products. If a tubular metal base having a diameter of 500 mm or more is manufactured and subjected to the above method for coating the inner or outer surface of the base, the weight and volume of the metal base which should be rotated at high velocity while maintaining a tubular shape are increased, and thus working becomes very dangerous, mechanical energy cost is increased, and parts of a mechanical device are easily worn, resulting in increased maintenance cost.
Furthermore, an extrusion process or an injection process requires an increase in the size of a mechanical device, undesirably increasing the manufacturing cost. As well, methods of controlling uniform heating and polymer behavior have not yet been developed.
Currently useful is a method of bonding both ends of a polyimide film to each other thus producing a tubular belt having a large diameter.
However, the tubular belt resulting from bonding of the film suffers because mechanical and electrical properties of the bonded portion may vary depending on the type of adhesive used for the bonded portion and the degree of overlap of both ends of the film. In a laser printer, it is thus difficult to uniformly transfer a toner and defective rates may be increased. Also, because a seam exists on the bonded portion, it may come into contact with an electronic device such as a photoreceptor drum of a laser printer and thus damage may occur during operation of the device. Hence, the development of a novel large seamless tubular belt is urgently required.
As well, in the case where the belt obtained by applying the polymer resin on a base and performing drying and heat treatment has a large diameter, it may be curled in its width direction, undesirably bending predetermined portions thereof. Furthermore, such curling may incur the meandering motion on a rotator, and ultimately, a case in which the belt breaks may occur. Therefore, there is a need to prevent the curling of the belt.